1. Field of the Invention
The present invention relates to a wave gear drive, particularly to a wave gear drive having a tooth profile that enables high ratcheting torque while also maintaining continuous meshing.
2. Description of the Prior Art
Since the wave gear drive drive was first invented by C. W. Musser (see U.S. Pat. No. 2,906,143), various types of wave gear drives have been invented by many researchers, including Musser and the present inventor. There have also been various inventions relating just to the tooth profiles used in wave gear drives. For example, one of the present inventors has proposed making the basic tooth profile an involute tooth profile (see JP-B 45-41171), and a method of designing a tooth profile in which the addendum profiles for wide contact between the rigid internal gear and flexible external gear are derived using a rack approximation of the meshing between the two gears (see JP-A 63-115943 and JP-A 64-79448). There has also been proposed an invention for avoiding interference between rack-approximated tooth profiles (see JP-A 7-167228).
In wave gear drives with high reduction ratios in which the number of the teeth of the two gears exceeds, for example, 160, what is called ratcheting may occur during high negative torque operation. This led one of the present inventors to propose a tooth profile that can prevent ratcheting while at the same maintaining continuous contact (see WO No. 2005/043006). In that disclosure, the deflection amount of the major axis of the elliptical rim neutral line of the flexible external gear at a cross-section of the flexible external gear perpendicular to the axis at an arbitrarily selected location in the tooth trace direction is set at 2κmn(κ>1), that is, positive deflection, and in the cross-section, the meshing of the teeth of both gears is approximated by rack meshing to obtain the moving route of the teeth of the external gear moved by the rotation of a wave generator, and the basic tooth profile of the two gears is defined by utilizing the curved portion of the moving route from the major axis of the moving route to the tooth departing side.